Method for transmitting measurement reports in a mobile communications system

ABSTRACT

A service node is provided in a mobile communications network which collects radio link measurement reports which are transmitted to the service node by mobile stations. The mobile stations transmit the measurement reports in encapsulated form, in the form of SMS messages, in order to prevent the interception of the measurement report by the serving base station. The service node is able to perform handover decision algorithms using the measurement reports collected from the mobile stations in order to determine appropriate radio access nodes to be allocated to the mobile stations.

FIELD OF THE INVENTION

This invention relates to mobile communications, in particular to thetransmission of radio resource signalling reports from mobile stationsin a cellular communications system, and to the handling thereof withinthe system.

BACKGROUND OF THE INVENTION

In known mobile communications systems, such as the GSM (Global Systemfor Mobile communications), it is known for mobile stations to takeradio link measurements during progress of a call, and to report thesemeasurements to the serving base station. The base scion uses thesedownlink measurement reports in order to determine when a handover isrequired.

Handover is initiated by the base station using radio sub-systemcriteria (signal strength level, link quality, link distance, etc) aswell as network directed criteria (e.g. current traffic loading percell, maintenance requests, etc).

In addition, current networks such as GSM networks include a mobileswitching center (MSC), a second generation component in the form of alarge, central switch.

Third generation systems are proposed in which various levels of serviceare provided and in which the MSC functionality is provided in adistributed processing environment, rather than in the form of a centralswitch.

It would be desirable to provide a more flexible and sophisticatedapproach to radio resource allocation. It would also be desirable toprovide for the re-use of existing mobile network elements, inparticular base stations, whilst providing enhanced radio resourcesignalling functionalities.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention there is provided amethod of transmitting signalling reports from a mobile station to aserving base station in a cellular communications system comprising anetwork infrastructure and a plurality of base stations connectedthereto, said method comprising transmitting radio measurement reportsintended for use by said serving base station to allocate a radioresource to said mobile station, and transmitting a radio resourcesignalling report intended for use by a service node in said networkinfrastructure to allocate a radio resource to said mobile station.

This aspect of the invention allows radio resources to be allocated bythe serving base station when appropriate, whilst also allowing radioresources to be allocated by a service node higher in the networkhierarchy in other circumstances. This prevents excessive signallingload in the network, whilst allowing additional parameters not availableto the base station to be taken into account when allocating radioresources in these other circumstances.

In accordance with a further aspect of the invention there is provided amethod of transmitting signalling reports from a mobile station to acellular communications system comprising a plurality of base stationsincluding a base station serving said mobile station via a radio link,said method comprising encapsulating a radio resource signalling reportbefore transmission over said radio link, such as to prevent saidserving base station from intercepting said radio resource signallingdata.

This aspect of the invention provides a method whereby radio resourcesignalling reports may be transmitted transparently through the servingbase station, and onwards to further elements in the system. Theencapsulation is preferably by means of a mobile-organizing SMS message,which allows existing radio interface functionality to be used toconceal the radio resource signalling report from the base station.

In accordance with a yet further aspect of the invention there isprovided a cellular communications system comprising a plurality of basestations for conducting communications with mobile stations via a radiointerface, and a service node for collecting radio resource signallingreports generated by mobile stations when in connected mode in saidsystem, said system comprising means for receiving said reports fromsaid plurality of base stations and for routing same to said servicenode.

This aspect of the invention provides for the collection and use ofradio resource-related data at the service node, to allow radio resourceallocation to be conducted by said service node on the basis of suchradio resource signalling reports. For example, the service node mayperform handover decision algorithms on the basis of the data containedin the radio resource signaling reports, along with other data such asdata specifying bandwidth, cost and/or quality of service requirementsfor the mobile stations.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described withreference to the accompanying drawings, wherein:

FIG. 1 is a schematic block diagram of a prior art mobile communicationsnetwork;

FIG. 2 is a schematic block diagram of a mobile station for use inrelation to the present invention;

FIG. 3 is a schematic block diagram of a mobile communications system inaccordance with the present invention; and

FIG. 4 is a schematic diagram illustrating functionality provided inaccordance with the present invention.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

A GSM network, referred to as a public land mobile network (PLMN), isschematically illustrated in FIG. 1. This is in itself known and willnot be described in detail. A mobile switching centre (MSC) 2 isconnected via communication links to a number of base station controller(BSCs) 4. The BSCs 4 are dispersed geographically across areas served bythe mobile switching centre 2. Each BSC 4 controls one or more basetransceiver stations (BTSs) 6 located remote from, and connected byfurther communication links to, the BSC. Each BTS 6 transmits radiosignals to, and receives radio signals from, mobile stations 8 which arein an area served by that BTS. That area is referred to as a “cell”. AGSM network is provided with a large number of such cells, which areideally contiguous to provide continuous coverage over the whole networkterritory. Indeed, a number of GSM networks may operate in the sameareas to provide overlapping coverage.

The mobile switching centre 2 is also connected via communications linksto other mobile switching centres in the remainder of the mobilecommunications network 10, and to other networks such as a publicservice telephone network (PSTN), which is not illustrated. The mobileswitching centre 2 is provided with a home location register (HLR) 12which is a database storing subscriber authentication data including theinternational mobile subscriber identities (IMSIs) which are unique toeach mobile station 8. An IMSI consists of a mobile country code (3decimal digits), a mobile network code (2 decimal digits) and a mobilesubscriber code (up to 10 decimal digits) identifying a subscriberwithin a particular network. The IMSI is also stored in the mobilestation in a subscriber identity module (SIM) (to be described below)along with other subscriber-specific information.

The mobile switching centre is also provided with a visitor locationregister (VLR), not shown, which is a database temporarily storingsubscriber authentication data for mobile stations active in its area.

In addition, the MSC is connected to a short message centre (SMC) 14 forhandling the transfer of short messages addressed to and from mobilestations within the network. The short message service (SMS) is apoint-to-point message service as specified in GSM TechnicalSpecification 03.40. A user of a mobile station 8 may generate amobile-originating SMS message by input to a Man Machine Interface (MMI)(e.g. a keypad) of the mobile station 8, and transmit the message, alongwith a destination address, to the servicing BTS 6. The message isforwarded transparently to the MSC 2, which directs the message on tothe SMC 14. The SMC 14 generally holds the message and handles theonward transmission to the terminating station corresponding to thedirectory number specified in the SMS message by the user of the mobilestation 8.

When switched on within coverage of the mobile network, the mobilestation has two possible modes, namely idle mode and connected mode.Both of these are described in GSM Technical Specification 05.08.

In idle mode, the mobile station 8 measures radio sub-system downlinkperformance and signal strengths received from surrounding cells. Themobile station 8 selects a preferred cell according to a cell selectionalgorithm, and informs the network via a signalling channel of itsselection. Occasionally, when the mobile station moves to a new cellsite, the mobile station transmits a location update to the mobilenetwork via a signalling channel.

When in connected mode, the mobile station 8 initiates a callestablishment procedure and is allotted a dedicated channel (a“connection”) for the transfer of voice and/or data traffic over theradio interface. Be dedicated channel includes a main traffic channel(TCH) for carrying the voice or data traffic, and a low-rate signallingchannel (the Slow Associated Control Channel, SACCH). When in connectedmode, the mobile station continuously performs radio measurements fromthe serving cell BTS and from neighboring cell BTSs. These measurementsare regularly reported to the serving cell BTS on the SACCH. The mobilestation can report measurements relating to a number of candidate targetcells in addition to the measurements relating to the serving cell.These measurements allow the serving BSC to decide when and whereto thehandover of a given mobile station in connected mode is to be initiated.The BSC intercepts the measurement reports generated by the mobilestation and sent on the SACCH part of the dedicated channel.

It is also possible for the mobile station 8 to send, and receive, shortmessages (SMS messages) when in connected mode. Such short messages arethen sent over the SACCH part of the dedicated channel assigned to themobile station, and are differentiated from signalling (in particular,the measurement reporting signalling) transmitted over the SACCH bymeans of a different link identifier (SAPI). The signal 8 messages areallotted SAPI 0, whilst short messages are allotted SAPI 3. Themobile-originating short messages are not intercepted by the BSC, butare transmitted to the MSC, which generally directs the short messagesusing the destination address in the short message header to the SMC 14.

FIG. 3 schematically illustrates an embodiment of the present invention,in which re-use of GSM-type BSCs 4 and BTSs 6, as well as at least partof the GSM radio interface, is possible, whilst a distributed processingnetwork infrastructure, using intelligent network (IN)-typefunctionality, replaces the prior art elements associated with andincluding the MSC 2.

In the arrangement of this embodiment of the invention, the BSCs 4 ofone connectivity provider are connected to a first service access node100, whereas those of a second connectivity provider are connected to asecond service access node 102.

Each of the service access nodes 100, 102 have connections to serviceprovision, mobility management, switching and other connection elements,not illustrated. The service access nodes 100, 102 are interconnectedusing an ATM link 104.

In addition, a service node 106 is connected to each of the serviceaccess nodes 100, 102, using signalling links. The service node 106 isprovided with a database 108. The service node 106 is adapted to performpredefined handover algorithms in order to make handover decisions basedon parameters stored in database 108.

The data stored in database 108 includes, for all currently-activesubscribers in each of the areas covered by the two connectivityproviders, data relating to the following:

1. Radio link quality. Radio link measurement is performed for thecurrent downlink in the mobile station 8, and for the current uplink inthe serving BTS 6. The measurements include, for example, bit errorrate, delay, delay jitter, change in quality of service, link lossprobability and the time before link loss.

2. A list of target radio access nodes. This is needed to determine thecell to which the radio link should be handed over to. The list isaccompanied by information regarding the node capacity and nodeoccupation.

3. Personal subscriber profile and service information, includingbandwidth requirements, quality of service requirements, access rights,priority and preference lists, environment selection, providerselection, etc.

4. Operational criteria, which include all the quasi-static parameters(congestion and load control related parameters) required to identifythe need for handover.

The mobile station 8 performs radio link measurements for both theservicing cell and the neighbouring cells during connected mode. Inaddition to the mobile station being adapted for transmitting thesemeasurements in a conventional GSM-type measurement report as signallingon the SACCH to the serving BTS, the mobile station is adapted toencapsulate radio resource measurement reports in short messages whichare addressed to the service node 106. The mobile-organizing shortmessage is constructed by the mobile station 8 using an originatingaddress/destination address header combination identifying to theservice access node 100 that the short message contains radio linkmeasurement data, instead of a user-defined short message. This ensuresthat the service access node 100 transmits the measurement report shortmessage to the service node 106, rather than the short message centre(not shown) provided in the intelligent network functionality.

Furthermore, since the measurement report is encapsulated as a shortmessage, the measurement report is not intercepted by the servingBTS/BSC, which would otherwise be the case if the measurement reportwere transmitted as normal signalling on the SACCH. This takes thedecision to attempt a handover out of the sole control of the BSC, andallows handover decisions to be made in the service node 106.

During connected mode, the transmission of measurement reports as normalsignalling on the SACCH to the serving BTS/BSC generally occurscontinually, such that normal handover decisions may then be made by theBSC 4.

When the mobile station has particular requirements e.g. bandwidthand/or quality of service, the SMS-encapsulated measurement reports armtransmitted by the mobile station instead of, or in addition to, thenormal signalling measurement reports, so as to allow radio resourceallocation decisions to be made by the service node 106.

The mobile station may be adapted to automatically transmit anSMS-encapsulated measurement report in response to detecting whenpredetermined service requirement criteria are met (or not met).

Alternatively or in addition, the mobile station may transmit anSMS-encapsulated measurement report on receipt of a request from theservice node 106. The service node transmits such a request when otherpredetermined service requirement criteria are met.

The service node 106 can thus, on receipt of a measurement report, makehandover decisions based on parameters not available to the individualBSCs, for example the personal profile and service information.

FIG. 4 schematically illustrates a situation in which handover betweentwo connectivity providers is possible, and in which the mobile terminalreports basic measurement data to the service node database 108. Mobileterminal 8 is in the vicinity of seven BTSs 6 having frequency channelnumbers 835, 822, 788, 821, 780, 800 and 830 respectively. The signalstrength measurements (between −106 dBm and −80 dBm) made by the mobileterminal are converted into corresponding quality index numbers (between0 and 26), and these quality index numbers are encapsulated, along withthe Base Station Identification codes and frequency channel numbers, ina mobile-originating SMS message which is transmitted automatically onthe SACCH by the mobile terminal 8 to the serving BTS 6. The message istransmitted transparently onwards through the serving BSC 4, into thenetwork, represented by box 110, and into the service node database 108.

The measurement reporting data encapsulated in the short messages isthus sufficient to precisely identify base stations that are visible tothe mobile station 8 by means of the base station identification codes,and their associated signal strengths. The service node 106 may decide,on executing a handover algorithm using this measurement data, that ahandover should be executed from the serving BTS (frequency channelnumber 788) belonging to one connectivity provider to a second BTS(frequency channel number 800) belonging to a second connectivityprovider. The handover, under instruction from the service node 106, isthen performed in the network in accordance with known handoverprocedures.

A decision to handover a connection may be made based on criteria suchas bandwidth (in the case where the mobile station has multiplebandwidth capabilities), quality of service and/or cost associated witheach of the different access nodes provided by the connectivityproviders. The SMS message may include data relating to the currentrequirements of the handset and/or the subscriber. For example, the SMSmessage may include identifiers for preferred connection providers,bandwidth requirements, cost limits, hardware and software versionnumbers of the handset, etc.

In the example described in relation to FIG. 4, the measurement reportsencapsulated in the SMS message contained only radio quality indexnumbers for each of the BTSs in the vicinity of the mobile station. Itis envisaged that other parameters useful for performing handoverdecisions could also, or alternatively, be encapsulated in the SMSmessage. For example, the data may include, for the serving cell, thetime slot number, the base station colour code, the global cell ID, thereceive quality, the receive signal level and/or the number of neighbourcells. Similar data could be provided for each of the neighbour cells,subject to optimisation to minimise signalling load within the network.

A service node is provided in a mobile communications network whichcollects radio link measurement reports which are transmitted to theservice node by mobile stations. The mobile stations transmit themeasurement reports in encapsulated form, namely in the form of SMSmessages, in order to prevent the interception of the measurement reportby the serving base station.

The service node is able to perform handover decision algorithms usingthe measurement reports collected from the mobile stations in order todetermine appropriate radio access nodes to be allocated to the mobilestations.

It is to be mentioned that handover decisions made by the service node106 need not be initiated only by the service node 106 on receipt of theSMS-encapsulated reports. A handover request may be directed by themobile station 8 to the service node 106. In this case, when the mobilestation initiates the handover request, it encapsulates a measurementreport as an SMS message directed at the service node 106, whichperforms the handover decision algorithm to determine which radio accessnode would best serve the mobile station.

In the above-described embodiments, the measurement report isencapsulated as a mobile-originating SMS message, to ensure that themeasurement report is not intercepted by the serving BTS/BSC. It isenvisaged that other modes of encapsulation would also be possible inorder to prevent interception of a measurement report by the servingBTS/BSC. For example, the measurement report may be carried using anenvelope and/or a message discriminator recognized at the servingBTS/BSC such that the serving BTS/BSC acts as a transparent relay forthe measurement report and allowing the measurement report to reach theservice node 106. A unique envelope definition could be provided for theencapsulation of such a measurement report which is recognized by theBTS/BSC interface in the network and by the service access node(s), suchthat it is directed to the service node 106.

Furthermore, the present invention is not limited to the transmission ofmeasurement reports to the service node 106. Alternative radio resourcesignalling data, for example only user preferences, or user requirementsor handover requests alone, could also be encapsulated and sent in asimilar manner.

Although a particular mobile station has been described above as anexample, the mobile stations may be any or all of:

-   -   personal digital assistants,    -   cellular telephones,    -   satellite telephones,    -   video phones,    -   facsimiles,    -   portable personal computers, etc.

It should be mentioned that the present invention is not limited toarrangements in which GSM-type BSCs and BTSs are re-used. Other cellularnetwork arrangements, in particular third generation systems, would alsobenefit from use of the present invention.

It is envisaged that further variations and modifications may beemployed without departing from the scope of the present invention.

1. A cellular communications system comprising: a plurality of basestations configured to conduct communications with mobile stations via aradio interface, wherein the mobile stations are used by subscribers; astorage system arranged to receive and store first data derived fromradio resource signalling reports generated by mobile stations when inconnected mode in the cellular communications system, wherein thecellular communications system is arranged to route the radio resourcesignalling reports from the mobile stations via the plurality of basestations to the storage system, and wherein the storage system isconfigured to store second data associated with the subscribers; and aservice node arranged to: receive data from the storage system for usein performing handover decisions, wherein the received data includes atleast a portion of the first data and at least a portion of the seconddata; process the received data so as to allocate a radio resource tothe mobile station, wherein the radio resource is allocated byselecting, from base stations for which radio resource measurements havebeen received from the mobile station, a base station for handover atleast in part on the basis of both the first data and the second data;and transmit data identifying the allocated radio resource to at leastone of the base stations.
 2. The system of claim 1, wherein the dataassociated with the subscriber includes a personal subscriber profileand/or service information.
 3. The system of claim 2, wherein thepersonal subscriber profile and/or service information includes at leastone of bandwidth requirements, quality of service requirements, accessrights, priority and preference lists, environment selection, hardwareand software version numbers of the associated mobile station, preferredconnection providers, and cost limits associated with the subscriber. 4.The system of claim 1, wherein the service node is arranged to requestdata from the storage system in response to receipt of data from one ofthe mobile stations.
 5. The system of claim 1, wherein the service nodeis arranged to transmit a resource signalling report request to at leastone of the mobile stations.
 6. The system of claim 1, wherein the systemis arranged to transmit a resource signalling report request to themobile station in response to a change in service conditions for themobile station.
 7. The system of claim 1, wherein the radio resourcesignalling reports are encapsulated in the form of an SMS message. 8.The system of claim 7, further comprising means for extracting the radioresource signalling reports from SMS messages received from the mobilestations.
 9. The system of claim 1, wherein the radio resourcesignalling reports comprise data indicative of downlink quality and/orneighbor cell signal strength.
 10. The system of claim 1, wherein theradio resource signalling reports comprise data specifying the currentrequirements of the mobile station.
 11. The system of claim 10, whereinthe current requirements include at least one of bandwidth,signal-to-noise ratio, radio path loss, cost, and quality of servicerequirements.
 12. The system of claim 10, wherein the currentrequirements include bandwidth, signal signal-to-noise ratio, radio pathloss, cost, and quality of service requirements.
 13. A method ofallocating radio resources to a mobile station used by a subscriber in acellular communications system, wherein the cellular communicationssystem comprises a plurality of base stations including a base stationserving the mobile station via a radio link, and wherein the cellularcommunications system has access to stored data for use in performinghandover decisions, wherein the stored data includes first data derivedfrom radio resource measurement data for each of a plurality of basestations surrounding the mobile station and second data associated withthe subscribers, wherein the second data is different from the firstdata, the method comprising: receiving a handover request in response toconditions satisfying one or more predetermined criteria; retrieving atleast some of the stored data in response to receipt of the handoverrequest, wherein the retrieved data includes at least a portion of thefirst data and at least a portion of the second data; processing theretrieved data so as to allocate a radio resource to the mobile station,wherein the radio resource is allocated by selecting, from base stationsfor which radio resource measurement data is included in the storeddata, a base station for handover at least in part on the basis of boththe first data and the second data; and transmitting data identifyingthe allocated radio resource to at least one of the base stations. 14.The method of claim 13, further comprising transmitting radio resourcemeasurement reports to the cellular communications system and storingdata indicative of the same for use in the allocation of radioresources.
 15. The method of claim 13, wherein the radio resourcemeasurement reports are transmitted during a dedicated channel trafficconnection for the mobile station.
 16. A method of allocating radioresources to a mobile station in a cellular communications system,wherein the cellular communications system comprises a plurality of basestations including a base station serving the mobile station via a radiolink, and wherein the cellular communications system has access tostored data for use in performing handover decisions, the methodcomprising: receiving a handover request in response to conditionssatisfying one or more predetermined criteria, wherein the handoverrequest is encapsulated as an SMS message so as to prevent the servingbase station from intercepting the radio resource signalling report;retrieving at least some of the stored data in response to receipt ofthe request; processing the retrieved data so as to allocate a radioresource to the mobile station; and transmitting data identifying theallocated radio resource to at least one of the base stations.
 17. Aservice node for allocating radio resources to a mobile station used bya subscriber in a cellular communications system, wherein the cellularcommunications system comprises a network infrastructure and a pluralityof base stations for conducting communications with mobile stations viaa radio interface, wherein the network infrastructure comprises astorage system arranged to store data for use in performing handoverdecisions, wherein the storage system is configured to store first dataderived from radio resource measurement data for each of a plurality ofbase stations surrounding the mobile station and second data associatedwith the subscriber, and wherein the service node is arranged to:receive data from the storage system for use in performing handoverdecisions, wherein the received data includes at least a portion of thefirst data and at least a portion of the second data; process thereceived data so as to allocate a radio resource to the mobile station,wherein the radio resource is allocated by selecting, from base stationsfor which radio resource measurement data is included in said storeddata, a base station for handover at least in part on the basis of boththe first data and the second data; and transmit data identifying theallocated radio resource to at least one of the base stations.
 18. Acellular communications system comprising: a plurality of base stationsconfigured to conduct communications with mobile stations via a radiointerface, wherein the mobile stations are used by subscribers; aplurality of mobile stations, wherein each mobile station is arranged togenerate radio resource measurement reports when in connected mode inthe cellular communications system, and wherein the radio resourcemeasurement reports include radio resource measurement data for each ofa plurality of base stations surrounding the mobile station; a storagesystem arranged to receive and store first data derived from the radioresource measurement data in the radio resource measurement reportsgenerated by mobile stations when in connected mode in the cellularcommunications system, wherein the cellular communications system isarranged to route the radio resource measurement reports from the mobilestations via the plurality of base stations to the storage system, andwherein the storage system is configured to store second data associatedwith the subscribers; and a service node arranged to: receive data fromthe storage system for use in performing handover decisions, wherein thereceived data includes at least a portion of the first data and at leasta portion of the second data; process the received data so as toallocate a radio resource to the mobile station, wherein the radioresource is allocated be selecting, from base stations for which radioresource measurements have been received from the mobile station, a basestation for handover at least in part on the basis of both the firstdata and the second data; and transmit data identifying the allocatedradio resource to at least one of the base stations.